The invention described herein relates to a method and apparatus for the measurement and characterization of pass through flux (PTF) of magnetic materials. The invented process comprises the use of various configurations of magnets in order to generate a magnetic field that emulates the open-loop situation found in magnetron sputtering (with xe2x80x9copen-loopxe2x80x9d referring to a situation in which magnetic lines of force are generated by a source or sources, and passed through at least two materials of which one is gas (e.g., air) or vacuum). The invented process is also capable of determining the PTF uniformity, which corresponds to the uniformity of the magnetic field distribution and the magnetic properties of the material.
Magnetron sputtering is widely used in the semiconductor and microelectronic industries to produce thin films. Magnetron sources increase the percentage of electrons that cause ionizing collisions by utilizing magnetic fields to help confine the electrons near the target surface. As a result magnetron sputtering processes can utilize current densities at the target of 10-100 mA/cm2, compared to about only 1 mA/cm2 for DC-diode diode configurations (see S. Wolf and R. N. Tauber, xe2x80x9cSilicon Processing for the VLSI Eraxe2x80x9d, volume 1, pp. 456). However, when magnetic sputtering targets such as cobalt, nickel or iron and their alloys are used in the magnetron sputtering machines, they tend to shield the sputtering cathode""s magnetic field. Magnetic sputtering targets can thus reduce PTF (with PTF being a parameter that measures the percentage of magnetic field transmitted through a magnetic material). Because of this, the efficiency of the sputtering process is reduced. In addition, low PTF can cause other problems such as less uniform thin films and shorter target life. For purposes of interpreting this disclosure and the claims that follow, the terms xe2x80x9cmagnetxe2x80x9d and xe2x80x9cmagneticxe2x80x9d are defined as follows. The term xe2x80x9cmagnetxe2x80x9d indicates an object that is itself a so-called xe2x80x9cpermanent magnetxe2x80x9d or an electromagnet. A xe2x80x9cpermanent magnetxe2x80x9d being defined in accordance with the art to be a magnet that retains a remnant magnetic field in the absence of an external magnetizing field. The term xe2x80x9cmagneticxe2x80x9d refers to an object that is either itself a magnet, or that is magnetized when it is in magnetic contact with a magnet or an electric field. Thus, the term xe2x80x9cmagnetic target materialxe2x80x9d encompasses target materials that are magnetized by interaction with a magnet, such as, for example, target materials comprising one or more ferromagnetic substances.
FIGS. 1-4 illustrate a problem which can occur with low PTF. Specifically, FIG. 1 illustrates an ideal situation which can occur if PTF is optimized, and shows a target 100 exposed to uniform lines of magnetic flux from a source 110. FIG. 2 shows an enlarged view of a portion of target 100 after exposure to the PTF of FIG. 1, and shows a wide cavity 112 corresponding to an erosion profile of the target 100. FIG. 3 illustrates an non-ideal situation which can occur if PTF is low and non-optimized, and shows a target 200 exposed to non-uniform lines of magnetic flux from source 110. FIG. 4 shows an enlarged view of a portion of target 200 after exposure to the PTF of FIG. 3, and shows a narrow cavity 212 corresponding to an erosion profile of the target 200.
As the use of magnetic materials becomes more prevalent in the semiconductor and microelectronics industry, the demand for characterization and understanding of the uniformity and magnetic properties of the materials in open-loop situations is becoming increasingly important. However, there is no universally recognized method to accurately characterize the magnetic properties, such as PTF, in a fashion that produces consistent and reproducible measurement data for users of the materials.
Although not widely used, one method for determining PTF is the ASTM standard F1761-96. In the ASTM method, a horseshoe-shaped magnet is used as the magnetic source and a single Hall sensor is used to measure the magnetic field strength. The ASTM standard suggests measuring 5 points by rotating the target in a 30xc2x15 degree interval, and then calculating the average value of the 5 points. Because this method only measures 5 points covering 120 degrees of the material, the uniformity information of a magnetic material cannot be determined adequately. Additionally, the ASTM method only measures one magnetic flux vector parallel to the material surface. Therefore, the flux and PTF information of the material is oversimplified and very limited. Furthermore, the reproducibility and repeatability (Gage RandR) of the ASTM measurements are poor.
Another method for determining PTF of a material utilizes a single ring magnet at one side of the material and a detector at another side of the material to measure magnetic field strength along a z-axis of the magnetic field. The detector can be moved relative to the target. The only measurements made by the detector are along the z-axis.
It is desirable to develop an apparatus and measurement method that not only provides reliable and consistent information about PTF and uniformity, but which is also capable of characterizing PTF in various configurations.
An apparatus of the present invention can be used for determining the pass through flux of magnetic materials, and comprises one or more magnetic field sensors arranged to collect field strength data of a magnetic field passing through a magnetic material. An exemplary apparatus comprises three Hall sensors arranged in such a way as to collect field strength data of all of the x, y, z axis directions of a field passing through a magnetic material. The apparatus also comprises a magnet, or arrangement of magnets, placed beneath the material being characterized, and includes a mechanism whereby the magnetic material can be mapped by the movement of any one or combination of: the magnetic field source or sources, the Hall probes and the magnetic material.
A method of the present invention comprises the use of various configurations of magnets in order to generate a magnetic field that emulates the open-loop condition found in magnetron sputtering. In one embodiment of this invention, the magnet configuration comprises the use of a solid round magnet within a ring-shaped magnet. The magnets are arranged in such a way that the flux flows from the ring to the solid magnet or vice versa. In another embodiment, a single ring-shaped magnet is used. In yet another embodiment, a small ring-shaped magnet is placed within a larger ring-shaped magnet.
The invention can comprise measuring magnetic field strengths a certain distance above a magnetic material in the x, y and z directions. The field strength measured in each of these three directions can be used individually, or combined together, to create a flux or PTF map. Such map can provide reliable and reproducible information regarding the magnetic properties and uniformity of the magnetic material. The map can be further interpreted based on statistical analysis to provide a method of PTF certification.